1. Field of the Invention
The present invention relates to an ARP server that is used in realizing a communication according to IP over ATM or the like.
2. Description of the Related Art
The Internet employs TCP/IP (transmission control protocol/Internet protocol) as its standard protocol. On the other hand, efforts are now being made to introduce the ATM (asynchronous transfer mode) technology into networks. To this end, the IETF (Internet Engineering Task Force) is now studying the protocol called "IP over ATM" to enable communications according to TCP/IP on ATM networks.
In the Internet, if the IP address of a terminal as a party to communicate with is known, one can communicate with that party according to TCP/IP. In an ATM network, however, even if the IP address of a party to communicate with is known, a communication cannot be made unless the ATM address of that terminal is known. In view of this, to allow a host application to perform a communication without being aware of the use of an ATM network, IP and ATM prescribes an address resolution technique for correlating an IP address with an ATM address and a procedure for setting an ATM connection.
IP over ATM will be outlined below with reference to FIGS. 21A and 21B. As shown in FIG. 21A, an ATM network where communications are performed according to IP over ATM is provided with a ATMARP (ATM address resolution protocol) having an ATMARP table which is a correlation table between IP addresses and ATM addresses for all terminals that are to perform communications.
For example, when terminal A starts an IP communication with terminal B, first of all terminal A sends a setup message to an ARP server as shown in FIG. 21A. Upon reception of the setup message from terminal A, the ARP server sets an ATM connection (VCC: virtual channel connection) and sends a call reception message to terminal A.
Upon reception of the call reception message, terminal A sends an ARP request packet including the IP address of terminal B by using the ATM connection thus set. Upon reception of the ARP request packet, the ARP server finds the address corresponding to the IP address included in the packet, i.e., the ATM address of terminal B by searching the ATMARP table. The ARP server transmits, to terminal A, an ARP relay packet in which the thus-found ATM address is set.
After acquiring the ATM address of the terminal of the party to communicate with by the above procedure (after address resolution), terminal A transmits a setup message to terminal B by using the ATM address thus acquired and starts to transmit IP packets when receiving a call reception message from terminal B.
As described above, Ip over ATM is constructed based on the existence of the ATMARP server which returns one ATM address for one IP address. Therefore, even where a plurality of circuits are set a receiving terminal and an ATM network, a calling terminal can acquire the ATM address of only one of those circuits from the ATMARP server. If that circuit is busy, a call cannot be established even if the other circuits are available.
Similarly, where a receiving terminal is a terminal on a wide area LAN network that is connected to a certain ATM network at plural locations, there may occur an even that a call cannot be established because the ATM addresses of the other connection points are unknown. In this case, there is even a possibility that a call is established with a route of a high connection charge in spite of the existence of a less expensive communication route.
The above problems is not limited to IP over ATM, and similar problems occur in LAN emulation for allowing an exchange, via an ATM network, of data that is transferred on a LAN such as an Ethernet or a token-ring network, and LE ARP (LAN emulation ARP) for converting a MAC (media access control) address into an ATM address.
Further, in the DNS (domain name service) of the current Internet using TCP/IP, an IP address is acquired from a domain name as an address of a terminal to communicate with. A current DNS server cannot accommodate a request that one IP address should be accessed in the daytime and the other in the night-time.